The present invention relates to a snubber device for use in a grapple. The grapple is intended for use in a skidder mechanism which is utilized for the movement of logs and other similar type material in rough terrain.
The prior art snubber devices require periodic adjustment, tightening and lubrication. Due to these requirements, a skidder was out of service during the down time required for such maintenance.
Prior art devices of this type are exemplified by U.S. Pat. Nos. 3,525,547 and 3,560,040. In U.S. Pat. No. 3,525,547 metal bushing supports are carried concentrically with casing members with the supports having bonded to their outer surfaces elastomer bushings that fill the space between the support elements and the cylindrical casings. In a relaxed condition, a bushing has an outer surface that is tapered slightly at one end and has a small annular surface groove. The bushings are pressed axially into the respective casings so that their respective outer surfaces frictionally engage the inner cylindrical surface of the casing. It is particularly noted that an evaporative type of lubricant is provided for inserting the bushing and that a more permanent type of lubricant is used to increase wear characteristics of the bushing.
The arrangement includes an upper bushing fixed against movement with respect to the boom of the skidder and a lower bushing fixed against movement relative to a housing support. Due to this arrangement, a movement is permitted so as to overcome the frictional resistance between the bushings and their casings. Frictional resistance between the bushings and the casings is increased or decreased by confining or releasing pressure on the bushings so as to prevent free oscillation about the axis of the grappler attachment to the boom of the machine.
U.S. Pat. No. 3,560,040 is quite similar in disclosure with respect to the bushing structure and contains more detail of the connection of the structure to the grappler hooks.
Accordingly, the prior art snubbers can be characterized as having rubber bushings contained in casings that are connected to a boom and a boom support, of a skidder, respectively. An outer surface is frictionally and resiliently engaged with the cylindrical walls of the casings. The prior art snubbers support the load lifted by the grappler due to the inner connection of the support plates of the snubber and the grapple. This arrangement causes the prior art snubbers to periodically need adjustment, tightening and lubrication.